Field of the Invention
The present invention relates to a wavefront measurement apparatus and a wavefront measurement method.
Description of the Related Art
In manufacturing of optical systems formed of a lens alone or a plurality of lenses, manufacturing errors such as an eccentric error and a surface shape error may be generated on each lens surface. Manufacturing errors may lead to reduction in imaging performance of an optical system.
For measurement of transmitted wavefront aberration in a subject optical system, axial wavefront aberration is generally measured because it can be measured with a simple configuration. In recent years, however, along with the increase in precision of optical systems, measurement needs are growing for axial wavefront aberration as well as off-axis wavefront aberration.
Off-axis wavefront aberration includes information that cannot be obtained by axial wavefront aberration. By acquiring data on off-axis wavefront aberration, the number of clues for analyzing imaging performance and manufacturing errors in a subject optical system is increased. For example, highly accurate analysis can be performed on the eccentricity amount of the subject optical system.
Examples of apparatus for measuring off-axis wavefront aberration include a wavefront aberration measurement apparatus disclosed in Japanese Patent Publication No. 5452032. In the wavefront aberration measurement apparatus disclosed in Japanese Patent Publication No. 5452032, light beams are applied from a position corresponding to an off-axis object point of an objective lens (lens to be measured). Parallel light beams exit from the objective lens, but the parallel light beams are inclined from an optical axis of the objective lens.
In a wavefront aberration measurement apparatus disclosed in Japanese Patent Publication No. 5452032, a Shack-Hartmann sensor is held by a stage that is movable in one axis direction and a goniostage. The stage and the goniostage are used to tilt and shift the Shack-Hartmann sensor, thereby adjusting the orientation and position of the Shack-Hartmann sensor and enabling the inclined parallel light beams to be received by the Shack-Hartmann sensor.